When I used the lvcreate cmd in my system, it blocked for a long
time. My OS kernel version is linux-2.6.29, is there any bug?

There is a bug somewhere. Your block device is hanging. You don't
mention what kind of block device and what driver are used for your
PVs. It would only be an LVM problem if the block device was itself
an LVM device. :-)
For instance, if your block device is iSCSI, and the SAN server is
down, or your block device is DRBD and the link is slow (has
happened to me), or your block device is a disk that is frantically
playing with bad sectors (has happened to me also), then LVM
would "hang".
--
Stuart D. Gathman <stuart bmsi com>
Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.